Semiconductor devices and other types of microelectronic devices can include a microelectronic die attached to a ceramic chip carrier, organic printed circuit board, lead frame, or other type of interposing structure. The dies can be attached to interposing structures using Direct Chip Attach (DCA), flip-chip bonding, or wire-bonding to electrically connect the integrated circuitry in the dies to the wiring of the interposing structures. Typical DCA or flip-chip methods, for example, include depositing very small bumps or balls of a conductive material (e.g., solder) onto the contacts of a die. The bumps are then connected to corresponding contacts or pads on an interposing structure.
FIG. 1, for example, is a partially schematic, isometric illustration of a portion of a conventional flip-chip assembly 10 including a microelectronic die 20 positioned for attachment to a substrate 30. The die 20 includes a plurality of conductive bumps 22 arranged in an array along an active side of the die 20. The substrate 30 includes a front surface 31 and a dielectric mask or layer 32 carried by the front surface 31. The dielectric mask 32 includes an aperture or opening 34 extending lengthwise along a medial portion of the mask 32. The substrate 30 also includes a plurality of contacts or traces 36 located at the front surface 31 and arranged in a pattern corresponding at least in part to the arrangement of conductive bumps 22 on the die 20. A solder ball 38 or other conductive coupler is disposed on each contact 36. The contacts 36 and solder balls 38 are accessible through the aperture 34 for coupling to corresponding conductive bumps 22. More specifically, during attachment the die 20 is inverted or “flipped” such that the active side bearing the conductive bumps 22 is superimposed with corresponding solder balls 38 and/or contacts 36 on the substrate 30, and a suitable reflow process is used to electrically and mechanically connect the die 20 to the substrate 30. An underfill material (not shown) may then be disposed in the gap between the die 20 and substrate 30 to protect the components from environmental factors (e.g., moisture, particulates, static electricity, and physical impact) and to enhance the mechanical attachment of the die 20 to the substrate 30.
The underfill material is typically dispensed into the gap by injecting the underfill material along one or two sides of the flip-chip device, and the underfill material is drawn into the gap by capillary effects. One potential drawback with the foregoing approach, however, is that it may result in a vulnerable mechanical connection between the die 20 and the substrate 30. For example, when the underfill material flows into the gap between the components, air bubbles, air pockets, and/or voids may form within the underfill material. The trench region around the aperture 34 is particularly susceptible to such voids because of the large volume of underfill material required to fill this area. During subsequent high temperature processes, the air trapped in these regions may expand and force the die 20 away from the substrate 30, damaging the mechanical and/or electrical connections between these components. Another drawback with this approach is that the underfilling method may be very time-consuming because the relatively large gap between the die 20 and substrate 30 takes time to fill, and the volume of fill material in the gap takes time to cure. This can significantly increase the overall time required for manufacturing the assembly.
Another drawback with the foregoing approach is that not all the solder balls 38 may make contact with the corresponding conductive bumps 22 of the die 20. For example, the solder balls 38 must typically be fairly large (e.g., about 80 μm) to extend between the bumps 22 and the corresponding contacts 36. In some cases, however, some of the solder balls 38 may be misshapen or smaller than normal and, accordingly, a gap may exist between these solder balls 38 and the corresponding conductive bumps 22. During the reflow process, this gap may not seal and the result may be an open circuit between the die's conductive bump 22 and the corresponding solder ball 38 and contact 36.
In light of the foregoing potential drawbacks, existing processes are time-consuming and may create at least some faulty packaged devices. In order to increase the efficiency and overall throughput of the manufacturing process for such devices, it is desirable to increase the robustness of both the mechanical and electrical connections between microelectronic dies and the structures to which they are attached.